Click above images to check out an inexpensive audio adapter (allows you to use XLR professional microphones with your iPhone), and Video Stabilizers for handheld iPhone shooting.

Below is Filmic Pro, the best App for your iPhone. It allows you to manually control focus and exposure, shoot up to 4K, and 50mbps at 1080 (similar to high end broadcast news cameras). It's a $10 purchase at the App store. Now available for both Android and iPhones. Click below for more info.